Devices such as the RCA DTC-100 allow for a HDTV broadcast to be viewed on an analog TV set. This is what is commonly known as a down converter which looses much of the HDTV signal detail when creating a NTSC signal. The present invention enables recording a SDTV (Standard Definition TV) or a HDTV (High Definition TV) digital signal, carried in compressed form, on a standard definition, analog (NTSC) video recorder, with the recording being essentially a digital recording. This is accomplished with no information thrown away and with a recording process, which is lossless.
Many articles (HDTV's Future Out of Focus, Jul. 31, 1998, Stewart Jennison of Messenger-Inquirer) discuss conversion of HDTV signal to an analog signal.
Integrated circuits or chips on the market today perform various functions with analog and digital SDTV and HDTV signals such as converting analog SDTV and HDTV signals to digital and vice versa. Other ICs perform MPEG compression and decompression of digital HDTV and SDTV signals. Still other Ics perform conversion and compression of audio signals. As one example, the Philips device SAA7114H provides for decoding of an analog PAL/NTSC/SECAM video signal to supply a digital component (Y, R-Y, B-Y) version of the input signal This IC and many others which are capable of such processing can be found on the internet web site for the respective companies. As another example, Texas Instrument chips THS8133 and THS8134 provide for digital to analog conversion of a digital HDTV signal. These and other similar chips provide a useful function for converting analog video to digital while other chips in the same product lines convert digital video to analog, which can be found in the discussion of the present invention. Motorola Super-Chip DSP56366 is a generalized digital signal processing IC which is capable of compression and decompression of digital audio signals. Program ROMs are available for several audio functions, for example decompression of MPEG or Dolby compressed audio signals. This chip provides a useful function for audio decompression, which can be found in the discussion of the present invention. C-Cube chip CLM4700 performs digital video encoding of MPEG digital video signals and, as such, can be useful for video compression as an element of the present invention. C-Cube also has available companion chips which perform decompression of compressed video signals.
It is known to convert CCIR 601 type digital video signal and AES/EBU audio signals to NTSC/PAL/SECAM analog audio and video for recording on existing analog video tape machines, with the subsequent conversion of the played back analog signals to digital Such systems are sold to enable the use of existing analog recording machines in CCIR 601 digital systems, thereby eliminating the need to replace the existing analog recording machines with new digital recording machines. The recorded signal is however an analog video signal and is subject to typical analog recording degradation such as added distortion and noise. This process of converting a digital signal to analog whereby the analog version is recorded is unlike the present invention which as will be explained in more detail uses a standard analog recorder to record a video and audio signals in digital form. The prior art system of converting to analog for recording works reasonably well because a CCIR 601 digital video signal contains only the same amount of information (i.e. image detail) as a standard analog NTSC/PAL/SECAM video signal. Thus CCIR 601 signals may be converted to analog and back with little loss of image detail, but with each conversion adding noise and distortion. Thought of in another way, the bandwidth of the analog signal necessary to carry an analog version of a CCIR 601 digital signal is compatible with analog NTSC/PAL/SECAM bandwidth standards In addition, while CCIR 601 allows for several audio channels, typically only two are used, which is compatible with the two analog audio channels which are typically provided in analog systems.
Unfortunately, the amount of image detail contained in any of the standard HDTV signal is far in excess of that of a CCIR 601 digital signal, and when such HDTV signals are converted to analog the resulting analog signal bandwidth is far in excess of that which is compatible with NTSC/PAL/SECAM standards and equipment. Consequently the aforementioned system of converting to analog and back to allow existing analog equipment to be used with HDTV signals will not work without a severe loss of image detail. Further, most HDTV audio signals are typically 4 or more channels with existing analog equipment typically providing capability for only two analog channels. Consequently, HDTV audio channels in excess of that provided in the existing analog equipment cannot be accommodated.